The present invention relates generally to video communications system, and more specifically to a video communications system in which motion-compensated interframe prediction coding and decoding principles are employed to reduce the rate of transmitted signals.
In a video communications system, a technique known as interframe predicting coding at the transmit end is employed to discard frames in order to set an upper limit on the transmission bit rate which would otherwise exceed that limit as a result of rapidly moving images. At the receive end of the system, discarded frames are created by repeatedly displaying a previous frame. The shortcoming of this technique is that jerkiness arises due to the repetition of same frames.
An interpolation technique is described in "Motion-Adaptive Interpolation For Videoconference Pictures", A. Furukawa et al., ICC '84, Links for The Future, Science, Systems & Services for Communications, IEEE International Conference on Communications, May 14-17, 1984 RAI Congress Centre, Amsterdam, The Netherlands, Proceedings, Volume 2, pages 707 to 710. According to this technique, an interframe predicted error signal and a motion vector are transmitted to a receive end where a representative vector is derived from the transmitted vectors and used for motion-compensating for a repeated frame to eliminate jerkiness.